MINNEAPOLIS  The gradual warming of the Upper Midwest could cut the duck population in half as early as 2050, according to a new study published in the journal BioScience.

The study looked at how climate change could affect the Upper Midwest, where North America's best duck breeding grounds are, over the next 50 to 100 years.

The area, known as the prairie pothole region, produces 50 percent to 80 percent of the continent's ducks and contains an estimated 5 million small ponds spread across the Dakotas, western Minnesota and Iowa, northeastern Montana and three Canadian provinces. Even though the area is notorious for wet and dry spells, it is large enough for waterfowl to adapt and migrate to other ponds with enough water and cover.

That would end if climate change increases average temperatures across the entire prairie pothole region, said Carter Johnson, a professor of ecology at South Dakota State University who co-authored the study.

He said most of the area would become too dry for ducks and other birds. Wetlands might remain only in the fringes of the region, in western Minnesota and northwestern Iowa, he said.

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Johnson and researchers from Minnesota and Montana reached their conclusions after studying 95 years of climate data and using hydrologic models to simulate changes to the Northern Great Plains during this century.

Study co-author Glenn Guntenspergen, a research ecologist with the U.S. Geological Survey in Duluth, said the area would still have occasional wet years, but they would be much less frequent. That would lead to lower water levels, longer dry periods and no water for years in many shallow wetlands.

He said that if the most productive waterfowl breeding areas in the Dakotas become marginal, the next-best habitat for birds will be on the eastern and northern edges of the pothole region, including western Minnesota and northwestern Iowa.

Most wetlands have been drained and would need to be restored in those areas, he said, adding that he believes federal conservation managers may need to begin spending more money on wetlands restoration there.

The study's predictions left Duluth conservationist Dave Zentner dumbfounded. Zentner coordinated a rally for ducks, wetlands and clean water in April that drew an estimated 4,000 people to the state Capitol.

He said wetland losses should concern hunters and anyone else who cares about trumpeter swans, gulls, terns, bitterns, night herons and other wildlife that depend on wetlands.

"I would hope that duck hunters would take this seriously and realize that this is not far-fetched theory," he said. "This is a real threat and the country needs to develop policies for it."